Laser source device, extreme ultraviolet lithography device and method

ABSTRACT

A device includes a laser source, an amplifier, an optical sensor and a spectrometer. The laser source is configured to produce a seed laser beam. The amplifier includes gain medium and a discharging unit. The discharging unit is configured to pump the gain medium for amplifying power of the seed laser beam. The optical sensor is coupled to the amplifier and configured for sensing an optical emission generated in the amplifier while the gain medium is discharging. The spectrometer is coupled with the optical sensor and configured to measure a spectrum of the optical emission.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 16/242,093, filedJan. 8, 2019, now U.S. Pat. No. 10,624,196, issued Apr. 14, 2020, whichapplication claims priority to U.S. Provisional Application Ser. No.62/737,873, filed on Sep. 27, 2018, the entire contents of which arehereby incorporated herein by reference in their entireties.

BACKGROUND

In semiconductor fabrication processes, increased density of integratedcircuits has increased the complexity of processing and manufacturingICs. There is a need to perform lithography processes with higherresolution. One of the leading lithography techniques is an extremeultraviolet (EUV) lithography. Others include X-Ray lithography, ionbeam projection lithography, and electron-beam projection lithography.EUV light with a wavelength around 5-100 nm or less can be used inphotolithography processes to produce extremely small patterns onsemiconductor wafers.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic diagram of a device in accordance with someembodiments of the present disclosure.

FIG. 2 is a schematic diagram of the laser source in FIG. 1 inaccordance with some embodiments of the present disclosure.

FIG. 3 is a schematic diagram of the amplifier component in FIG. 1 inaccordance with some embodiments of the present disclosure.

FIG. 4 is a flow chart of a method suitable to be applied on the devicein FIG. 1, FIG. 2 and FIG. 3, in accordance with some embodiments of thepresent disclosure.

FIG. 5 is a schematic diagram illustrating a spectrum of the opticalemission measured by the spectrometer in accordance with someembodiments of the present disclosure.

FIG. 6 is a schematic diagram illustrating another spectrum of theoptical emission measured by the spectrometer in accordance with someembodiments of the present disclosure.

FIG. 7 illustrates a waveform diagram of a waveform of the opticalemission plotted by the spectrometer in accordance with some embodimentsof the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

The terms used in this specification generally have their ordinarymeanings in the art and in the specific context where each term is used.The use of examples in this specification, including examples of anyterms discussed herein, is illustrative only, and in no way limits thescope and meaning of the disclosure or of any exemplified term.Likewise, the present disclosure is not limited to various embodimentsgiven in this specification.

Although the terms “first,” “second,” etc., may be used herein todescribe various elements, these elements should not be limited by theseterms. These terms are used to distinguish one element from another. Forexample, a first element could be termed a second element, and,similarly, a second element could be termed a first element, withoutdeparting from the scope of the embodiments. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

FIG. 1 is a schematic diagram of a device 100, in accordance with someembodiments of the present disclosure.

As illustratively shown in FIG. 1, the device 100 includes a lasersource 110, an amplifier 120, an optical sensor 130, a spectrometer 140,a processor 150, a beam transport system (BTS) 160, a laser focus unit170 and an extreme ultraviolet (EUV) generating vessel 180. In someembodiments, the device 100 is a laser produced plasma extremely ultraviolet (LPP-EUV) light source which is capable of generating an extremeultraviolet light EUVL. The extreme ultraviolet light EUVL has awavelength about 5 nm to about 100 nm. In some embodiments, the extremeultraviolet light EUVL has a wavelength about 13.5 nm.

As illustratively shown in FIG. 1, in some embodiments, the device 100further includes optical components 190, and the extreme ultravioletlight EUVL is guided through optical components 190 onto a wafer WF. Insome embodiments, the device 100 is an extreme ultraviolet lithographyequipment, which is capable of generating the extreme ultraviolet lightEUVL and utilizing the extreme ultraviolet light EUVL to form a patternonto the wafer WF.

The laser source 110 is configured to produce a seed laser beam SLB.Reference is further made to FIG. 2. FIG. 2 is a schematic diagram ofthe laser source 110 in FIG. 1, in accordance with some embodiments ofthe present disclosure. As illustratively shown in FIG. 2, in someembodiments, the laser source 110 includes a pre-pulse laser generator111, a main pulse laser generator 112, a beam combiner 113 and apre-amplifier 114. The pre-pulse laser generator 111 is configured toproduce a pre-pulse laser beam PLB. The main pulse laser generator 112is configured to produce a main pulse laser beam MLB. The pre-pulselaser beam PLB has a wavelength different from a wavelength of the mainpulse laser beam MLB. In some embodiments, the wavelength of thepre-pulse laser beam PLB and the main pulse laser beam MLB are in arange from about 9 μm to about 12 μm. In some embodiments, the pre-pulselaser generator 111 and the main pulse laser generator 112 can begas-discharge CO₂ laser generators. In other embodiments, other suitablelaser generators, for examples, an excimer or molecular fluorine laser,may be used for the pre-pulse laser generator 111 and the main pulselaser generator 112 shown in FIG. 2.

As illustratively shown in FIG. 2, in some embodiments, the beamcombiner 113 is configured for combining the main pulse laser beam MLBand the pre-pulse laser beam PLB onto one optical path to form the seedlaser beam SLB. In the embodiments illustratively shown in FIG. 2, theseed laser beam SLB is a combination of the main pulse laser beam MLBand the pre-pulse laser beam PLB. In some other embodiments, the seedlaser beam SLB includes one laser beam, for example the main pulse laserbeam MLB or the pre-pulse laser beam PLB, produced by one gas-dischargelaser generator. The pre-amplifier 114 is configured to enhance power ofthe seed laser beam SLB. In some embodiments, the pre-amplifier 114 isable to modulate the power of the seed laser beam SLB to about 1 kW toabout 5 kW.

As illustratively shown in FIG. 1, the seed laser beam SLB produced bythe laser source 110 transmits through the amplifier 120 to the beamtransport system (BTS) 160. Afterward, the seed laser beam SLB isutilized to excite a target droplet DP in the extreme ultravioletgenerating vessel 180 for producing the extreme ultraviolet light EUVL.In order to effectively excite a target droplet DP in the extremeultraviolet generating vessel 180, the seed laser beam SLB is requiredto have enough power. The amplifier 120 is utilized to amplify power ofthe seed laser beam SLB. In some embodiments, the amplifier 120 is ableto modulate the power of the seed laser beam SLB to about 5 kW to about15 kW.

As illustratively shown in FIG. 1, in some embodiments, the amplifier120 includes four stages of amplifier components 121, 122, 123 and 124positioned along an optical path of the seed laser beam SLB, but thepresent disclosure is not limited in this regard. The number andconfiguration of the amplifier 120 in following embodiments are givenfor illustrative purposes. In some other embodiments, the amplifier 120includes at least one amplifier component to amplify power of the seedlaser beam SLB.

The seed laser beam SLB after processed by the amplifier 120 istransmitted through the beam transport system 160 to the extremeultraviolet generating vessel 180. In some embodiments, the laser source110 and the amplifier 120 may be implemented at one location, forexample a ground floor or underground of a factory, and the extremeultraviolet generating vessel 180 and the optical components 190 may beimplemented at another location, for example a first floor or a secondfloor of the factory. In some embodiments, the beam transport system 160is configured to transport the seed laser beam SLB between two locationswith minimum leakage.

As illustratively shown in FIG. 1, in some embodiments, the laser focusunit 170 is disposed between the beam transport system 160 and theextreme ultraviolet generating vessel 180. The laser focus unit 170 isconfigured to make the seed laser beam SLB converge at a point preciselyto excite the target droplet DP in the extreme ultraviolet generatingvessel 180.

As illustratively shown in FIG. 1, in some embodiments, the extremeultraviolet generating vessel 180 includes a droplet generator 182, adroplet catcher 184, an extreme ultraviolet collector 186 and anintermediate focus unit 188. The droplet generator 182 is configured toprovide the target droplet DP. In some embodiments, the target dropletDP is a tin-doped droplet. The droplet catcher 184 is configured tocatch and remove the target droplet DP after being impacted by the seedlaser beam SLB. The target droplet DP excited by the seed laser beam SLBwill become laser-produced plasma, and the laser-produced plasma willproduce the extreme ultraviolet light EUVL in different directions. Theextreme ultraviolet collector 186 is configured to gather the extremeultraviolet light EUVL onto the intermediate focus unit 188. Theintermediate focus unit 188 is configured to make the seed laser beamSLB converge the extreme ultraviolet light EUVL onto one optical path.The extreme ultraviolet light EUVL converged by the intermediate focusunit 188 can be utilized by optical components 190 for extremeultraviolet lithography. As illustratively shown in FIG. 1, in someembodiments, the optical components 190 include at least one illuminatormirror and at least one reticle mask for forming a pattern on the waferWF.

In some embodiments, the optical sensor 130 is coupled to the amplifier120 and is configured for sensing an optical emission generated in theamplifier 120. As illustratively shown in FIG. 1, in some embodiments,the amplifier 120 includes four stages of amplifier components 121, 122,123 and 124. As a demonstrational example, the optical sensor 130 isdisposed in the amplifier component 122 of the amplifier 120. Asillustratively shown in FIG. 1, in some embodiments, the optical sensor130 is able to sense the optical emission at the second stage, i.e., theamplifier component 122, while the seed laser beam SLB is amplifying inthe four consequent stages of the amplifier 120.

In some other embodiments, the optical sensor 130 can be disposed atleast one of the amplifier components 121-124. For example, the opticalsensor 130 can be disposed in the amplifier component 121, 123 or 124 insome embodiments. Alternatively, two or more optical sensors can bedisposed two of more amplifier components 121-124. The optical sensor130 disposed in the amplifier component 122 in following embodiments aregiven for illustrative purposes. However, the disclosure is not limitedthereto. Reference is further made to FIG. 3. FIG. 3 is a schematicdiagram of the amplifier component 122 in FIG. 1, in accordance withsome embodiments of the present disclosure. As illustratively shown inFIG. 1 and FIG. 3, in some embodiments, the amplifier component 122 islocated between the amplifier component 121 and the amplifier component123. The amplifier component 122 receives the seed laser beam SLBamplified by the amplifier component 121. The amplifier component 122 isconfigured to further amplify the seed laser beam SLB and send the seedlaser beam SLB to the amplifier component 123.

As illustratively shown in FIG. 3, the amplifier component 122 includesa shielding 210, glass tubes GT1, GT2, GT3 and GT4, connection chambersCHB1, CHB2, CHB3 and CHB4, a discharging unit, gain medium GM and anultraviolet blocking cover 250. The shielding 210 is an external surfaceof the amplifier component 122. The glass tubes GT1, GT2, GT3 and GT4are disposed in the shielding 210 and configured to accommodate the gainmedium GM. In some embodiments, the glass tubes GT1, GT2, GT3 and GT4are quartz tubes. In some embodiments, the gain medium GM is a gasmixture includes carbon dioxide, CO₂, and nitrogen, N₂. In someembodiments, the gas mixture accommodated inside the glass tubes GT1,GT2, GT3 and GT4 further includes helium, He, for stabilizing the gasmixture. Helium is not utilized as an active gain medium. Thedischarging unit includes a power source 240 and electrodes 241 and 242disposed adjacent to the glass tubes GT1-GT4.

In some embodiments, the electrodes 241 are utilized as anode electrodesand the electrodes 241 are utilized as cathode electrodes 242 on each ofthe glass tubes GT1-GT4. The power source 240 provides radio-frequencysignals RF. The radio-frequency signals RF are applied on the electrodes241 and 242 disposed on opposite sides of each of the glass tubesGT1-GT4 for pumping the gain medium GM. In order to keep brevity of FIG.3, wirings for transmitting the radio-frequency signals RF between thepower source 240 to the electrodes 241 and 242 on the glass tube GT1 isillustrated, and similar wirings for transmitting the radio-frequencysignals RF to the electrodes 241 and 242 on the glass tubes GT2-GT4 arenot shown in FIG. 3. The radio-frequency signals RF are configured toboost an energy level of the gain medium GM in the glass tubes GT1, GT2,GT3 and GT4. When the seed laser beam SLB travels through the glasstubes GT1, GT2, GT3 and GT4, the seed laser beam SLB will absorb energyfrom the gain medium GM, such that the power of the seed laser beam SLBwill be amplified.

As illustratively shown in FIG. 3, the connection chambers CHB1, CHB2,CHB3 and CHB4 are configured to connect the glass tubes GT1, GT2, GT3and GT4 and guide the optical path of the seed laser beam SLB. Asillustratively shown in FIG. 3, in some embodiments, a fluid inlet GMiis implemented at the connection chamber CHB1 and a fluid outlet GMo isimplemented at the connection chamber CHB4. In some embodiments, thegain medium GM is provided from a gas pipeline, not shown in figures, tothe fluid inlet GMi. The gain medium GM flows from the fluid inlet GMito the fluid outlet GMo.

In the embodiment illustratively shown in FIG. 3, the amplifiercomponent 122 includes four glass tubes GT1-GT4 and four connectionchambers CHB1-CHB4 for connecting between the glass tubes GT1-GT4.However, the number and configuration of the glass tubes and theconnection chambers in the amplifier component 122 are given forillustrative purposes. In some other embodiments, the amplifiercomponent 122 includes at least one glass tube and correspondingconnection chambers. In some embodiments, the amplifier component 122may include twelve glass tubes or more for further amplifying the powerof the seed laser beam SLB.

As illustratively shown in FIG. 3, in some embodiments, the opticalsensor 130 is disposed in the amplifier component 122. There is at leastone opening formed on the shielding 210. As illustratively shown in FIG.3, there are six openings 211-216 formed on different positions on theshielding 210. As illustratively shown in FIG. 3, in some embodiments,an upper end of the optical sensor 130 is disposed inside the shielding130 and a lower end of the optical sensor 130 penetrates the shielding210 through the opening 211. The optical sensor 130 disposed in theshielding 210 of the amplifier component 122 is able to sense an opticalemission generated in the amplifier component 122 while the gain mediumGM is discharging, and the optical sensor 130 will generate an opticalemission signal SOES describing the optical emission. As illustrativelyshown in FIG. 3, the ultraviolet blocking cover 250 is disposed over theopenings 211-216 on the shielding 210 for blocking a leakage of the seedlaser beam SLB or the optical emission.

As illustratively shown in FIG. 3, in some embodiments, the opticalsensor 130 is disposed at the opening 211, which is relatively adjacentto the fluid inlet GMi and relatively away from the fluid outlet GMo. Inthis configuration illustratively shown in FIG. 3, the optical sensor130 is able to sense the optical emission adjacent to the fluid inletGMi, such that the optical emission signal SOES is highly related to aninlet flow rate of the gain medium GM. In some other embodiments, theoptical sensor 130 can be adjusted to be implement at different opening212-216 to sense the optical emission from different locations of theamplifier component 122, and the optical emission signal SOES canreflect more information about different conditions, e.g., an outletflow rate, of the amplifier component 122. In some embodiments, theoptical sensor 130 includes Optical Emission Spectrometry (OES) sensorhead. The Optical Emission Spectrometry sensor head is able to generatethe optical emission signal SOES with a sample rate about 10 samples persecond to about 15 samples per second.

As illustratively shown in FIG. 1 and FIG. 3, in some embodiments, anoptical fiber cable 132 is configured for transmitting the opticalemission signal SOES generated by the optical sensor 130 to thespectrometer 140. One end of the optical fiber penetrates through theultraviolet blocking cover 250 and is connected to the optical sensor130. Another end of the optical fiber cable 132 is connected to thespectrometer 140.

As illustratively shown in FIG. 1 and FIG. 3, the spectrometer 140 iscoupled with the optical sensor 130 and configured to measure a spectrumof the optical emission. The processor 150 is coupled with thespectrometer 140, and the processor 150 is configured to determine anoperational status of the amplifier 120 according to the spectrum of theoptical emission. Further details about how to determine the operationalstatus of the amplifier 120 according to the spectrum will be explainedand discussed in following paragraphs.

As illustratively shown in FIG. 1, in some embodiments, the processor150 is coupled to the spectrometer 140 and a storage medium 152. Invarious embodiments, the processor 150 is a central processing unit(CPU), an application specific integrated circuit (ASIC), a multi-coresprocessor, a distributed processing system, or a suitable processingunit. Various circuits or units to implement the processor 150 arewithin the contemplated scope of the present disclosure.

The storage medium 152 stores one or more program codes for performingsome tasks on the processor 150. For illustration, the storage medium152 stores program codes encoded with executable instructions forperforming some tasks on the processor 150. The processor 150 is able toaccess the program codes stored in the storage medium 152.

In some embodiments, the storage medium 152 is a non-transitory computerreadable storage medium encoded with, i.e., storing, a set of executableinstructions for performing aforesaid tasks on the processor 150. Insome embodiments, the non-transitory computer readable storage medium isan electronic, magnetic, optical, electromagnetic, infrared, and/or asemiconductor system (or apparatus or device). For example, the computerreadable storage medium includes a semiconductor or solid-state memory,a magnetic tape, a removable computer diskette, a random access memory(RAM), a read-only memory (ROM), a rigid magnetic disk, and/or anoptical disk. In one or more embodiments using optical disks, thecomputer readable storage medium includes a compact disk-read onlymemory (CD-ROM), a compact disk-read/write (CD-R/W), and/or a digitalvideo disc (DVD).

Reference is now made to FIG. 4. FIG. 4 is a flow chart of a method 400suitable to be applied on the device 100 in FIG. 1, FIG. 2 and FIG. 3,in accordance with some embodiments of the present disclosure. For easeof understanding, as an example, the method 400 is described below withreference to FIG. 1, FIG. 2 and FIG. 3.

For illustration, the method 400 in FIG. 4 includes operationsS402-S410. In operation S402, the laser source 110 is configured toproduce a seed laser beam SLB. In operation S404, the amplifier 120 isconfigured to amplify the power of the seed laser beam SLB. Duringoperation S404, as illustratively shown in FIG. 3 and FIG. 4, the powersource 240 applies the radio-frequency signals RF on the electrodes 241and 242 for pumping the gain medium GM. The seed laser beam SLB isdirected through the gain medium GM. The seed laser beam SLB absorb theenergy from the gain medium GM, such that the power of the seed laserbeam SLB is amplified. As illustratively shown in FIG. 3 and FIG. 4, inoperation S406, the optical sensor 130 disposed in the amplifiercomponent 122 senses the optical emission generated in the amplifiercomponent 122 while the gain medium GM is discharging. In operationS408, the spectrometer 140 measures the spectrum of the opticalemission. In operation S410, the processor 150 determines an operationalstatus of the amplifier 120 according to the spectrum of the opticalemission.

Reference is further made to FIG. 5, which is a schematic diagramillustrating a spectrum SP1 of the optical emission measured by thespectrometer 140, in accordance with some embodiments of the presentdisclosure. As illustratively shown in FIG. 5, in some embodiments, thespectrum SP1 of the optical emission indicates intensities of theoptical emission at different wavelengths. The spectrum SP1 reflects theoptical emission include different beam components at differentwavelengths mainly ranged from about 200 nm to about 1100 nm.

In some embodiments, the processor is configured to analyze the spectrumSP1 based on the waveform and a peak distribution of the spectrum SP1.As illustratively shown in FIG. 5, the spectrum SP1 has four peaksP1-P4. The peak P1 is located at about 315 nm corresponding to anemission band induced by carbon dioxide, CO₂. The peak P2 is located atabout 336 nm corresponding to an emission band induced by carbondioxide, CO₂. The peak P3 is located at about 357 nm corresponding toanother emission band induced by carbon dioxide, CO₂. The peak P4 islocated at about 375 nm corresponding to still another emission bandinduced by carbon dioxide, CO₂. The four peaks P1-P4 are listed fordemonstration. The processor 150 may capture and analyze further peaks,for example, peaks from about 300 nm to about 800 nm in the spectrum SP1for more details.

In some embodiments, the spectrum SP1 is a standard spectrum recordedwhen the device 100 and the amplifier 120 operating in a normal status.The spectrum SP1 can be stored in the storage medium 152 for reference.

Reference is further made to FIG. 6, which is a schematic diagramillustrating another spectrum SP2 of the optical emission measured bythe spectrometer 140, in accordance with some embodiments of the presentdisclosure. As illustratively shown in FIG. 6, in some embodiments, thespectrum SP2 of the optical emission indicates intensities of theoptical emission at different wavelengths. As illustratively shown inFIG. 6, the spectrum SP2 has corresponding four peaks P1-P4. The peak P1is located at about 315 nm corresponding to an emission band induced bynitrogen, N₂. The peak P2 is located at about 336 nm corresponding to anemission band induced by carbon dioxide, CO₂.

In some embodiments, when the spectrum SP2 is measured by thespectrometer 140, the processor 150 is configured to compare thespectrum SP2 in reference with the spectrum SP1 stored in the storagemedium 152. Because the spectrum SP2 is different from the spectrum SP1regard as the standard spectrum, the processor 150 is able to determinethat the device 100 or the amplifier 120 is currently in an abnormalstatus.

Compared to the spectrum SP1 regarded as the standard spectrum in FIG.5, an intensity of the peak P2 of the spectrum SP2 in FIG. 6 is lowerthan an intensity of the peak P2 of the spectrum SP1, and intensities ofthe peaks P1 and P3 of the spectrum SP2 in FIG. 6 is higher thanintensities of the peak P1 and P3 of the spectrum SP1. Accordingly, theprocessor 150 is able to determine that the abnormal status can berelated to an inlet flow rate of the gain medium GM is currently lowerthan a standard rate, or the abnormal status can be a ratio of thecarbon dioxide, CO₂ in the gas mixture of the gain medium GM is lowerthan a standard ratio. In some embodiments, the processor 150 is able toanalyze the abnormal status according to a difference between thespectrum SP2 in FIG. 6 and the spectrum SP1 in FIG. 5. In someembodiments, the processor 150 is able to analyze a setting of theradio-frequency signals RF, which are applied on the electrodes of theglass tubes GT1-GT4 in FIG. 3 for pumping the gain medium GM, accordingto the difference between the spectrum SP2 in FIG. 6 and the spectrumSP1 in FIG. 5.

Reference is further made to FIG. 7, which illustrates a waveformdiagram of a waveform WVF of the optical emission plotted by thespectrometer 140, in accordance with some embodiments of the presentdisclosure. In FIG. 7, the waveform WVF reflects an amplitude variationof the optical emission over time. The waveform WVF in a period P1between a time point T0 and another time point T1 reflects the amplitudevariation of the optical emission when the device 100 is operating.During the period P1, the laser source 110 and the amplifier 120 isactivated to work. The waveform WVF of the optical emission will have acharacteristic of a glowing light. The amplitude of the waveform WVFvaries up and down periodically in the period P1. It is assumed that thelaser source 110 and the amplifier 120 at the time point T1, and theamplitude of the waveform WVF during a period P2 returns to a low level,e.g., zero. It is assumed that the laser source 110 and the amplifier120 restarts at a time point T2. It can be observed that the waveformWVF during a period P3 starts to climb up to a high level. The waveformWVF during a period P4 will resume to a normal status, similar to theperiod P1, with the characteristic of the glowing light.

In some embodiments, the period P3 is regarded as an ignition phase ofthe laser source 110 and the amplifier 120. The ignition phase can beobserved in the period P3 of the waveform WVF because the optical sensor130, in some embodiments, including the Optical Emission Spectrometry(OES) sensor head with the sample rate about 10 samples per second toabout 15 samples per second. In some approaches, a rejected powerreturned from the amplifier 120 can be measured at an interface betweenthe laser source 110 and the amplifier 120, and the rejected power ismeasured at a sample rate about 1 sample every 12 seconds. In thoseapproaches, it is hard to observe the ignition phase in the rejectedpower returned from the amplifier 120 to the laser source 110. Asillustratively shown in FIG. 7, the waveform WVF during the period P3 ofthe optical emission plotted by the spectrometer 140 is able to reflectthe ignition phase of the laser source 110 and the amplifier 120. Theprocessor 150 is able to analyze the ignition phase of the laser source110 and the amplifier 120 according to the waveform WVF during theperiod P3.

The predetermined sequences, including the ascending numerical orderand/or the descending numerical order, are given for illustrativepurposes only. Various kinds of orders are within the contemplated scopeof the present disclosure.

For ease of understanding, the embodiments above are given with anapplication of fabricating two switches. The embodiments above are ableto be applied to fabricate a single switch or two more switches. Forillustrative purposes, the embodiments above are described asimplementing the switches. The present disclosure is not limitedthereto. Various elements are able to be implemented according to theembodiments above, and thus are the contemplated scope of the presentdisclosure.

In this document, the term “coupled” may also be termed as “electricallycoupled,” and the term “connected” may be termed as “electricallyconnected”. “Coupled” and “connected” may also be used to indicate thattwo or more elements cooperate or interact with each other.

In some embodiments, a device including a laser source, an amplifier, anoptical sensor and a spectrometer is disclosed. The laser source isconfigured to produce a seed laser beam. The amplifier includes gainmedium and a discharging unit. The discharging unit is configured topump the gain medium for amplifying power of the seed laser beam. Theoptical sensor is coupled to the amplifier and configured for sensing anoptical emission generated in the amplifier while the gain medium isdischarging. The spectrometer is coupled with the optical sensor andconfigured to measure a spectrum of the optical emission.

Also disclosed is a method that includes the operation below. A seedlaser beam is produced by a laser source. Power of the seed laser beamby an amplifier is amplified. An optical emission is sensed by anoptical sensor disposed in the amplifier. A spectrum of the opticalemission is measured. An operational status of the amplifier isdetermined according to the spectrum of the optical emission.

Also disclosed is a device that includes a laser source, an extremeultraviolet generating vessel, an optical component, an optical sensorand a spectrometer. The laser source is configured to produce a seedlaser beam. The seed laser beam being is directed to the extremeultraviolet generating vessel to form laser-produced plasma. Thelaser-produced plasma is configured to generate an extreme ultravioletlight. The extreme ultraviolet light transmitting through the opticalcomponent is utilized to in lithographing a wafer. The optical sensor isconfigured for sensing an optical emission generated while the seedlaser beam is amplified before entering the extreme ultravioletgenerating vessel. The spectrometer is coupled with the optical sensorand configured to measure a spectrum of the optical emission.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device, comprising: a laser source configuredto produce a seed laser beam; an amplifier comprising gain medium and adischarging unit, the discharging unit being configured to pump the gainmedium for amplifying power of the seed laser beam; an optical sensorcoupled to the amplifier and configured for sensing an optical emissiongenerated in the amplifier while the gain medium is discharging; and anextreme ultraviolet generating vessel, wherein the optical emission isutilized to excite a droplet in the extreme ultraviolet generatingvessel for producing an extreme ultraviolet light, the extremeultraviolet light is utilized to form a pattern onto a wafer.
 2. Thedevice of claim 1, further comprising: a spectrometer coupled with theoptical sensor and configured to measure a spectrum of the opticalemission; and a processor coupled with the spectrometer and configuredto determine an operational status of the amplifier according to thespectrum of the optical emission.
 3. The device of claim 1, wherein thegain medium is a gas mixture comprising carbon dioxide and nitrogen. 4.The device of claim 1, wherein the amplifier comprises: a plurality ofamplifier components positioned along an optical path of the seed laserbeam, the seed laser beam being sequentially amplified by the amplifiercomponents, the optical sensor is coupled to one of the amplifiercomponents.
 5. The device of claim 1, wherein the amplifier comprises: ashielding; and a glass tube disposed in the shielding and configured toaccommodate the gain medium, wherein the discharging unit comprises aplurality of electrodes disposed adjacent to the glass tube, and aradio-frequency signal is applied on the electrodes for pumping the gainmedium.
 6. The device of claim 5, wherein an opening is formed on theshielding, the optical sensor is disposed at least partially inside theshielding and through the opening.
 7. The device of claim 6, wherein anultraviolet blocking cover is disposed over the opening on the shieldingfor blocking a leakage of the seed laser beam.
 8. The device of claim 7,further comprising: a spectrometer coupled with the optical sensor andconfigured to measure a spectrum of the optical emission; and an opticalfiber cable configured for transmitting a signal of the opticalemission, a first end of the optical fiber penetrates through theultraviolet blocking cover and is connected to the optical sensor, asecond end of the optical fiber cable is connected to the spectrometer.9. The device of claim 5, wherein the gain medium flows from a fluidinlet to a fluid outlet, and the optical sensor is disposed relativelyadjacent to the fluid inlet and relatively away from the fluid outlet.10. A method, comprising: producing a seed laser beam by a laser source;amplifying power of the seed laser beam by an amplifier; sensing anoptical emission by an optical sensor disposed in the amplifier;exciting a droplet by the optical emission to produce an extremeultraviolet light; and utilizing the extreme ultraviolet light to form apattern onto a wafer.
 11. The method of claim 10, wherein the gainmedium is a gas mixture comprising carbon dioxide and nitrogen.
 12. Themethod of claim 11, wherein the amplifier comprises a plurality ofelectrodes and gain medium, and amplifying power of the seed lasercomprises: applying a radio-frequency signal on the electrodes forpumping the gain medium; and directing the seed laser beam through thegain medium.
 13. A method, comprising: producing a seed laser beam by alaser source; amplifying power of the seed laser beam by the amplifier;sensing an optical emission by an optical sensor disposed in theamplifier; measuring a spectrum of the optical emission; analyzing peakintensities under different wavelengths in the spectrum; and detectingan abnormal status of the amplifier according to the peak intensities.14. The method of claim 13, wherein the amplifier comprises a pluralityof electrodes and gain medium, and amplifying power of the seed lasercomprises: applying a radio-frequency signal on the electrodes forpumping the gain medium; and directing the seed laser beam through thegain medium.
 15. The method of claim 14, wherein one of the peakintensities corresponds to a gas component in the gain medium.
 16. Themethod of claim 15, wherein in response to that the one of the peakintensities is reduced, the abnormal status is detected, the abnormalstatus is related to an inlet flow rate of the gain medium, an outletflow rate of the gain medium, or a ratio of the gas component in thegain medium.
 17. The method of claim 15, wherein the gain medium is agas mixture comprising carbon dioxide and nitrogen.
 18. The method ofclaim 14, further comprising: analyzing a setting of the radio-frequencysignals applied on the electrodes according to the spectrum.
 19. Themethod of claim 13, wherein the optical emission is sensed by theoptical sensor disposed in the amplifier during an ignition phase of theamplifier.
 20. The method of claim 13, wherein the optical emission issensed by the optical sensor disposed in the amplifier during anignition phase of the laser source.